Flat gummed paper



' United States Patent No. 2,793,966.

United States Patent FLAT GUMMED PAPER Arnold Agulnick, Worcester,Mass., assignor to Dennison Manufacturing Company, Framingham, Mass, acorporation of Massachusetts No Drawing. Application October 25, 1957Serial No. 692,252

2 Claims. 01. 106-128 This invention relates to gummed sheet material,that is, sheet material having a coating of dry adhesive which can bemoistened with water to develop an adhesive tackiness which permits thesheet to be attached to another surface. Such coated sheets are commonarticles of commerce, gummed labels and postage stamps being commonexamples. Adhesives of this nature are commonlyv called remoistenableadhesives, glue or gum and these terms are herein used to include anynormally nontacky adhesive which can be activated with water.

Gummed sheet materials of this character have been troublesome in usebecause of their tendency to curl or roll up with changes in relativehumidity due to the unequal expansion and contraction of the adhesivecoating and of the backing sheet. This problem is particularlytroublesome in gummed sheets which receive printing for labels and thelike, which have to be run through printing presses in controlledregistration therewith. This dilficulty has necessitated printing roomswith controlled relative humidity.

A number of expedients have heretofore been attempted to correct thisproblem but with only partial success. Recently a new expedient has beendisclosed in This method involves the dispersion of minute particles ofsolid waterreactivatable adhesives in a. solvent solution of a secondgum which is also water-soluble. The solvent used for the dispersiondissolves the second or carrier gum which is pres'ent in a minorproportion when compared with the dispersed water-reactivatableadhesive, but in which the latter is not soluble. After coating anddrying, the minute solid particles of water-activatable adhesive arepresumably discontinuous in a matrix of the second gum. This methodproduces a gummed sheet of superior flatness but introduces its ownproblems. An important problem with this method is the necessity forobtaining the waterreactivatable adhesive in a very fine particle size,usually less than one mil. Such materials, being adhesive andmoisture-sensitive, are extremely difficult to grind and maintain inthis small particle size. Also this method requires substantial amountsof a second or carrier gum which is quite expensive when compared withthe watersensitive adhesive. Also, where the water-reactivatableadhesive is included as solid particles rather than deposited from awater solution, the glue is not as readily reactivated as is desirable.

The principal object of this invention is to provide superflat gummedsheet material, together with a method and coating composition formaking the same which will remain substantially flat even after repeatedchanges in relative humidity. Further objects are to provide superfiatgummed sheet material having an adhesive layer which is firmly bound tothe carrier sheet, which will not block or adhere to superposed sheetswhen stacked with other sheets of like material, which is readilyactivated with water, which is easily prepared, and which is relativelyinexpensive when compared with previous methods.

In accordance with this invention the improved superflat gummed sheetmaterial of the water-remoistenable type comprises a sheet having on oneside thereof a'po tentially adhesive dry film which when moistened withWater will adhere to a surface, said film comprising in discontinuousphase a multiplicity of minute particles of water soluble gum, saidparticles adhesively contacting the surrounding particles and the sheet,and a continuous phase of a polymeric film-forming binder joining saidpar ticles together and to the sheet, said binder being soluble in waterand also soluble in another solvent in which said water-soluble gum isnot soluble, said film being sulficiently open to permit rapidactivation by water. While the water-activatable gum is held insubstantially discontinuous phase, the gum particles or agglomerates docon;

tact and adhere to a slight extent to each other and to the support,thus contributing to film strength and to adhesion to the support.Indeed, if the binder be extracted with solvent, the gum remains as aporous, self-supporting film. The particles of water-reactivatable gumshould comprise a major portion of the total mass of the film.

Suitable binder resins include polyvinyl methyl ether,

i The above superflat gummed sheet material is made by a method whichcomprises dissolving a water-soluble binder in an incompletelywater-miscible solvent, dissolving water-activatable gum in water,dispersing the.

water solution in the binder solution, coating the resulting compositionon the sheet, and drying. After thecoat; ing has been dried the exposedsurface of the carrier sheet should be treated under tension accordingto techniques, well known in the prior art, to equalize thecont'ractioncaused by wetting the coated side.

In a further aspect the present invention includes coatable compositionfor preparing water-remoistenable gummed sheet material comprising adispersion of a water solution of a water-activatable gum dispersed in awater-immiscible solvent solution of a water-soluble; resinous binder,said gum exceeding by weight the amount;

of the binder.

To the naked eye the coatings of the present invention appear smooth andsubstantially homogeneous. However, microphotographs show that thecoatings, after drying, have particles of water-reactivatable adhesiveembedded in a water-soluble binder matrix. Both the binder and the gumare water-soluble, the gum particles are available for remoistening asis illustrated by the ease with which the film is made strongly tacky bymoistening.

As an example of this invention the following example is given:

Example I Polyvinyl methyl ether 7.5 Toluene 32.5

Animal glue (50% in water) Example 11 Polyvinyl methyl ether 7.5 Toluene32.5 Animal glue (60% in water) Example III N-butyl amine salt ofpolyvinyl acetate-maleic' anhydride copolymer 7.5 Toluene 75 Animal glue(50% in water) 75 The binder is dissolved in the toluene and a lowviscosity animal glue is separately dissolved in water and P ten ed.Dec- 15,1259.

maintained at a temperature of approximately 150 F. The glue solution at150 F. is added to the solvent solution of the binder with vigorousagitation.

The dispersion technique is critical in making coating according tothis'invention. The water-activatable adhesive or gum must make up amajor portion of the dried film and must be dispersed as a watersolution in a solvent solution of the water-soluble binder. Thedispersion must be a dispersion of the water-in-oil type with thesolvent phase as the continuous phase and the water as thediscontinuous. For this purpose the solvents used to dissolve the bindermust not dissolve the water-activatable gum and must be incompletelymiscible with water. Whether the solvent comprises a single liquid or amixture of liquids the only requirement is that it be sufficientlyimmiscible with water to keep the water solution in dispersed phase. Inaddition to the toluene shown above, benzene, n-butyl alcohol,cycloxhexanone, ethyl acetate, nitroethane, and nitropropane may be usedas binder solvents. The solvent or solvent mixture used to dissolve thebinder must show preferential solubility for the particular binder used;that is, in the presence of the solvent-water mixture a greater portionof the binder must dissolve in the solvent. Various starches, starchethers, dextrins and polysaccharides and mixtures thereof may be used inplace of or with the animal glue. It is desirable that the watersolution contain the highest possible solids commensurate with ease ofpreparation so that a minimum amount of water will be required. For thisreason it is desirable to use low viscosity glues and proteins. Variousmaterials such as solvent-soluble dispersing agents may be added toimprove the stability of the mixture.

The continuous phase binder must adhere to the gum and to the base onwhich it is coated. Since both the binder and the gum are water-solublethe gum is available to the water used in remoistening. Additionally itisbelieved that the film structure is open, porous, and sponge-like dueto the evaporation of the water and solvents as the coating is dried.This sponge-like structure is an additional aid in making thewater-activatable gum available for remoistening. In addition to aidingand providing the sponge-like structure of a coating the deposition ofthe gum from a water solution dispersed in the binder solution has anumber of other advantages. Gum which has been thoroughly digested anddissolved in water is more readily activated by remoistening and morequickly develops good tack. The wet gum, being adhesive as it dries,gives better internal binding of the film and to the support since itadhesively contacts the particles in association with the gum particles.While the gum particles may contact one another to some degree they arestill present in a substantially discontinuous phase. This bindingaction resulting from the wet glue permits a higher percentage of thedesired gum to be used, making a better and cheaper product. Again, theuse of a wet gum obviates the need for grinding gum into very fineparticles as taught in the prior art. When the water solution is heatedand then added to the solvent solution with vigorous agitation, the gumwill be dispersed with a very fine particle size and the resultingcoating will be glossy. On the other hand, when the water solution isadded cold to the solvent solution, the resultant coating will have adull mat finish due to larger particles of gum. By this means controlledparticle size can be obtained in the final coating without the need forgrinding dry gum.

It should be understood that this disclosure is for the purpose ofillustration only and that the invention includes all equivalents andmodifications which fall within the scope of the appended claims.

I claim:

1. The method of making a substantially non-curling gummed sheet of thewater-remoistenable type which comprises dissolving a water-solublebinder in a solvent, dissolving water-activatable gum in water,dispersing the water solution in the binder solution, coating theresulting composition on the sheet, and drying, the solvent beingsufi'iciently immiscible with water to keep the water solution isdispersed phase and possessing preferential solubility for said hinder,the weight of the gum exceeding the weight of the binder.

2. A coating composition for preparing water-remoistenable gummed sheetmaterial comprising a dispersion of a water solution of awater-activatable gum dispersed in a solvent solution of a water-solubleresinous binder, the solvent being sufficiently immiscible with water tokeep the water solution in dispersed phase and possessing preferentialsolubility for said binder, said gum exceeding by weight the amount ofthe binder.

References Cited in the file of this patent UNITED STATES PATENTS2,215,848 Bauer Sept. 24, 1940 2,365,020 Stillwell Dec. 12, 19442,577,821 Smith et a1 Dec. 11, 1951 2,793,966 Davis May 28, 1957

1. THE METHOD OF MAKING A SUBSTANITALLY NON-CURLING GUMMED SHEET OF THE WATER-REMOISTENABLE TYPE WHICH COMPRISES DISSOLVING A WATER-SOLUBLE BINDER IN A SOLVENT, DISSOLVING WATER-ACTIVATABLE GUM IN WATER, DISPERSING THE WATER SOLUTION IN THE BINDER SOLUTION, COATING THE RESULTING COMPOSITION ON THE SHEET, AND DRYING THE SOLVENT BEING SUFFICIENTLY IMMISCIBLE WITH WATER TO KEEP THE WATER SOLUTION IS DISPERSED PHASE AND POSSESSING PREFERENTIAL SOLUBILITY FOR SAID BINDER, THE WEIGHT OF THE GUM EXCEEDING THE WEIGHT OF THE BINDER. 